The present invention relates to a magnetic recording medium and magnetic recording-reproducing device, and particularly relates to a magnetic recording medium in which stiction between the magnetic recording medium and a head slider flying on the surface of the magnetic recording medium and mounted with a magnetic head for recording and reproducing information into/from the magnetic recording medium is prevented effectively so that crush or the like due to the stiction can be prevented, and magnetic recording-reproducing device having the magnetic recording medium.
Magnetic recording media such as hard disks have been conspicuously improved in areal density by improved techniques such as finer granulation of magnetic particles for forming magnetic recording layers, alteration of materials, and finer head processing. Further improvement in areal density will be expected in the future. However, the improved techniques adopted till now have elicited problems as to side fringes, crosstalk, etc. due to a limit of head processing and a spread of a magnetic field. Thus, the improvement in areal density using the background-art techniques has reached its limit.
As one of solutions to the problems, that is, as one of techniques which can improve the areal density of magnetic recording media, there have been proposed discrete track type magnetic recording media (for example, see JP-A-9-97419 or JP-A-2000-195042). A typical discrete track type magnetic recording medium has a magnetic recording layer formed with concentric track patterns, and a non-magnetic layer filled into concave portions between adjacent ones of the magnetic recording layer patterns so as to extend continuously in the track direction and separate the concentric track patterns from each other.
In magnetic recording-reproducing device having such a discrete track type magnetic recording medium, servo pattern regions serving as reference of tracking control for controlling a magnetic head to track on a desired track are formed all over the 360° circumference of the magnetic recording medium and, for example, at fixed angular intervals between adjacent ones of data track regions.
FIG. 2 is a schematic configuration diagram showing an example of a servo pattern region formed in a discrete track type magnetic recording medium. Servo pattern regions 21 are formed all over the 360° circumference of the magnetic recording medium and at fixed angular intervals between data track regions 20 and 20 adjacent to each other. Each servo pattern region 21 is chiefly constituted by a sync signal region (preamble region) 22, an address region 23 and a servo burst signal region 24. The sync signal region 22 serves to fix the reproduced waveform amplitude by means of an AGC circuit or to secure synchronization with a clock. The address region 23 includes a timing signal indicating the start position of a sector and serving as a reference position of each data track region 20, and an index identification signal. The servo burst signal region 24 serves to generate a position signal indicating a position in a track. Incidentally, the address region 23 includes a track number identification function for identifying the number of a track arranged in the radial direction of the disk and a sector number identification function for identifying the number of a servo pattern arranged in the circumferential direction of the disk.
The servo burst signal region 24 is a two-phase servo system typically constituted by four burst signal regions 24A, 24B, 24C and 24D. Amplitude differences between burst signals are calculated based on the pair of the first and second burst signal regions 24A and 24B and the pair of the third and fourth burst signal regions 24C and 24D. Thus, of the amplitude differences, portions high in linearity are connected to obtain a linear position error signal. Such servo pattern regions 21 serve as reference for the magnetic head to accurately trace tracks formed in the magnetic recording medium. Thus, high positioning accuracy is required for forming the servo pattern regions 21.
In manufacturing of a discrete track type magnetic recording medium having servo pattern regions and data track regions, a non-magnetic material is filled into concave portions of a predetermined concavo-convex pattern with which a magnetic recording layer is formed. Thus, the surface is made flat enough to suppress fluctuation in flying of a head slider mounted with a magnetic head. As a method of charging thus, a film formation technique such as sputtering to be used in the field of semiconductor manufacturing is used. However, when the film formation technique is used, the non-magnetic material is formed not only in the aforementioned concave portions but also on the upper surface of the magnetic recording layer. Thus, irregularities in high relief caused by the non-magnetic material formed as a layer on the magnetic recording layer are formed in the surface of the magnetic recording medium. Due to the irregularities in high relief, there occur problems as follows. That is, the flying height of the head slider mounted with the magnetic head and flying due to an air flow on the surface of the magnetic recording medium rotating at the time of recording-reproducing is made unstable, or the gap length between the magnetic head and the magnetic recording layer is increased (that is, the spacing loss between the magnetic head and the magnetic recording layer). Thus, the sensitivity is lowered or foreign matters are accumulated easily.
As a solution to the aforementioned problems, it is desired to flatten the surface of the magnetic recording layer while removing the non-magnetic material formed as a layer on the magnetic recording layer. A processing technique such as CMP (Chemical Mechanical Polishing), for example, used in the field of semiconductor manufacturing is used as such a flattening method. Typically a texture is formed in the surface of a magnetic recording medium so that stiction between the head slider and the magnetic recording medium is prevented by the effect of the texture. When the aforementioned CMP method or the like is used to make the surface of the magnetic recording medium too flat, the effect of the texture is not exerted sufficiency. Thus, there is a problem that the head slider is stuck onto the magnetic recording medium so that the magnetic head is crushed easily.
Particularly, with increase in areal density, the flying height of the head slider may be not higher than 10 nm. In such a case, the head slider and the magnetic recording medium are brought into intermittent contact with each other. In this state, when the surface of the magnetic recording medium is too flat, there is a problem that friction between the head slider and the magnetic recording medium increases so that the magnetic head is crushed easily for the same reason as mentioned above.
JP-A-2000-195042 proposes a solution to such a problem, in which a texture is formed in the flattened surface of a non-magnetic material, and stiction between a head slider and a magnetic recording medium is prevented by irregularities of the texture so as to prevent crush from occurring.
Although the magnetic recording medium disclosed in JP-A-2000-195042 has some effect in preventing the stiction of the head slider, it is necessary to add a step of forming a texture in the flattened surface of the non-magnetic material. Thus, there is a problem that the number of steps in the manufacturing process increases so as to increase the cost. In addition, in the magnetic recording medium manufactured thus, the flattened non-magnetic material remains on the surface of the magnetic recording layer. Thus, there is a problem that the gap length (synonymous with “spacing loss”: the same thing will be applied below) between the magnetic recording layer formed in the magnetic recording medium and the magnetic head is increased.